As one type of device for discharging a liquid material in the form of a droplet, there is known a device of striking a valve body against a valve seat to separate the liquid material from a distal end of a discharge port such that the liquid material is discharged as a droplet flying from the distal end. In that type of device, the valve body is driven in various manners.
For example, Patent Document 1 discloses a device of the type ascending a valve body by air pressure, and descending the valve body by a repulsive force of a spring. In the device of Patent Document 1, a piston attached to the valve body is slidably fitted in a driving chamber, and a spring (compressed spring) is disposed above the piston. An air chamber is formed under the piston and is connected to a compressed air source through a selector valve. A discharge chamber is formed under the driving chamber with interposition of a wall therebetween, the wall having a penetration hole through which the valve body is inserted. The valve body is movable in the discharge chamber, and a discharge port is formed in a lower surface of the discharge chamber. A liquid material is supplied under adjusted pressure to the discharge chamber from a reservoir. When the selector valve is operated to supply the compressed air to the air chamber, the piston is caused to ascend while contracting the spring, thereby opening the discharge port that has been closed by the valve body. Because the liquid material is in a state under pressure, the liquid material is ejected to the outside from a tip when the discharge port is opened. When the selector valve is operated to release the compressed air, which has been supplied to the air chamber, to the atmosphere, the valve body is caused to descend by the repulsive force of the contracted spring and to abut against an upper portion of the discharge port, which portion forms a valve seat, whereupon the valve body is abruptly stopped in a state closing the discharge port. As a result, the liquid material ejected from the distal end of the discharge port is discharged in the form of a droplet.
As another example, Patent Document 2 discloses a device of the type ascending a valve body by an electrical solenoid and descending the valve body by another (separate) electrical solenoid. In the device of Patent Document 2, a jetting member is disposed within a main container including a nozzle through which an adhesive is to be ejected, and two electrical solenoids for driving the jetting member are arranged coaxially with the jetting member at a position above the main container. A flange is formed on a core rod of second one of the two electrical solenoids, which is located at an upper position, and a spring for always biasing the jetting member toward an ejection inhibit position is engaged with the flange. When the first electrical solenoid is operated, the jetting member is moved from the ejection inhibit position to an ejection enable position. Because the adhesive is pressurized by compressed air, the adhesive is ejected from the nozzle, and an adhesive pool is formed at a nozzle tip. Then, when the second electrical solenoid is operated, the jetting member is moved from the ejection enable position to the ejection inhibit position while a biasing force of the spring is applied additionally, thereby causing a lower end portion of the jetting member to abut against a bottom surface of the main container. As a result, the adhesive pool formed at the nozzle tip is jetted.